SCAF (Series Connection through Apertures on Film) type photoelectric conversion apparatus is known as a typical example of photoelectric conversion apparatus in which a plurality of unit photoelectric conversion elements formed on the same substrate are connected in series.
In the SCAF type photoelectric conversion apparatus, a plurality of unit photoelectric conversion elements are formed on, for example, a flexible substrate having an insulating property, such that each of the unit photoelectric conversion elements is composed of a lower electrode, a photoelectric conversion layer consisting of a thin-film semiconductor layer, and an upper electrode, which are laminated in this order on the substrate. By electrically connecting the lower electrode of a certain unit photoelectric conversion element with the upper electrode of its adjacent unit photoelectric conversion element in a repeated manner, namely, by connecting the plural unit photoelectric conversion elements in series, a desired voltage may be established between the lower electrode of the first unit photoelectric conversion element and the upper electrode of the last unit photoelectric conversion element. In order to provide an alternating voltage of 100V as a commercial power source as a result of dc/ac conversion by an inverter, for example, the photoelectric conversion apparatus is desired to produce an output voltage of 100V or higher, and, in an actual apparatus, several tens of unit photoelectric conversion elements are connected in series.
The series connection of the unit photoelectric conversion elements is established by forming electrode layers and photoelectric conversion layer and patterning each of these layers, through a suitable combination of film-forming and patterning processes. A known example of photoelectric conversion apparatus will be now described in which a small number of unit photoelectric conversion elements are connected in series.
FIG. 7(a) is a plan view showing a conventional thin-film solar cell including series-connected electrodes formed on opposite surfaces of a substrate, and FIG. 7(b) is a cross-sectional view taken along lines x-X of FIG. 7(b). In FIG. 7(b), "n" is suffixed to reference numerals that denote adjacent unit photoelectric conversion element and adjacent electrodes.
A large number of unit photoelectric conversion elements are formed on one surface (that will be called "front surface") of a substrate 1 formed of a flexible insulating material, such that each if unit photoelectric conversion element is composed of a lower electrode layer, photoelectric conversion layer and an upper electrode layer that are laminated on each other. On the other surface (rear surface) of the substrate is formed a rear electrode consisting of a first connecting electrode layer and a second connecting electrode layer that are laminated on each other.
Initially, a lower electrode layer is formed on one surface of the substrate 1 through which connecting holes or apertures H1 are formed, and a rear electrode layer is formed on the other surface of the substrate 1. The lower electrode layer and the first connecting electrode layer overlap each other on the inner wall of each connection hole H1, so that these layers are electrically connected with each other. The lower electrode layer is subjected to laser beam machining for removing thin strip-like parts of the electrode layer to provide parting lines L1, so that the lower electrode layer is divided by the parting lines L1 into individual lower electrodes 2e having a desired shape. Then, current collecting holes or apertures H2 are formed through the substrate, lower electrode layer and the first connecting electrode layer. Subsequently, a photoelectric conversion layer is formed over the entire area of the substrate made of a-Si. With the opposite end portions of the substrate being covered by masks having a simple shape (e.g., rectangular shape), an upper electrode layer as a transparent electrode layer is formed on the substrate, using the above masks, so that the electrode layer does not extend over the connection holes H1. Then, a second connecting electrode layer is formed on the entire area of the rear surface of the substrate, such that the upper electrode layer and the second connecting electrode layer overlap each other on the inner wall of the current collecting holes H2, so that these layers are electrically connected with each other. Subsequently, the upper electrode layer and a laminate of the first and second connecting electrodes are subjected to laser beam machining so that the upper electrode layer is divided by parting lines L2 into individual upper electrodes 5e, and the first and second connecting electrode layer are divided by parting lines L3 into individual first and second connecting electrodes 3e, 6e.
As a result of the process as described above, the unit photoelectric conversion elements are connected in series such that current flows through the second connecting electrode 6e and first connecting electrode 3e on the rear side of the substrate, lower electrode 2e, photoelectric conversion layer 4p, and upper electrode 5e (namely, one unit photoelectric conversion element), current collecting hole H2, adjacent second connecting electrode 6en and first connecting electrode 3en, connecting hole H1 lower electrode 2en, photoelectric conversion layer 4pn and upper electrode 5en (namely, adjacent unit photoelectric conversion element), in the order of description.
In the known SCAF type photoelectric conversion apparatus as described above, the total area of the connecting holes and collecting holes that are non-power-generating regions can be made considerably smaller than the area of the unit photoelectric conversion elements and the area of the substrate, and therefore the ratio of the non-power-generating area to the overall substrate area, namely, area loss, can be considerably reduced. Also, the electrodes at the opposite ends of the series-connected unit photoelectric conversion elements, namely, external lead electrodes between which the output voltage is established, are located on the rear surface of the substrate, and thus do not provide non-power-generating regions, which greatly contributes to a reduction in the area loss. Furthermore, external leads are connected to the external lead electrodes on the rear surface, thus avoiding an increase in the non-power-generating region.
Another known example of photoelectric conversion apparatus similarly intended for a reduction in the area loss is disclosed in Japanese Patent No. 2,647,892. In this photoelectric conversion apparatus, a second rear electrode film, insulating film, first rear electrode film, semiconductor film and a light-receiving side electrode film are laminated in this order on a substrate. The electrical connection between the light-receiving side electrode film and the second rear electrode film is established through a contact hole formed through the insulating film, first rear electrode film and the semiconductor film, and electrical connection between the first rear electrode film and second rear electrode film is established through another contact hole formed through the insulating film, so that the unit photoelectric conversion elements are connected in series. In this photoelectric conversion apparatus, the second rear electrode film and the unit photoelectric conversion elements are disposed on the same surface of the substrate. Since the second rear electrode film provides output electrodes for connection with leads at the opposite ends of the series-connected unit photoelectric conversion elements, external leads must be connected to the output electrodes on the side of the light-receiving surface, and therefore the area loss cannot be sufficiently reduced. In the above-described SCAF type photoelectric conversion apparatus, on the other hand, the upper and lower electrodes of the unit photoelectric conversion elements are connected to the corresponding connecting electrodes or rear electrodes formed on the rear surface opposite to the light-receiving surface of the substrate, through apertures formed through the substrate. Thus, the output electrodes are located on the rear surface of the substrate, thus making it possible to connect external leads with these electrodes without increasing an area loss.
In the known photoelectric conversion apparatus, however, the connecting holes H1 need to be located outside the power-generating region (generally, in the peripheral portion of the substrate), and therefore the upper electrodes 5e are not formed on the opposite end portions of the substrate including the connecting holes H1, which provides non-power-generation regions R. Thus, area loss due to non-power-generating regions is not sufficiently reduced. Substantially no problem arises in principle where masks are formed over individual connecting holes H1 so as not to form the upper electrode layer in and around the connecting holes H1. However, in the case of a large-length substrate, in particular, the above manufacturing process tends to be complicated, resulting in a significant increase in the manufacturing cost, and is thus not employed.
While laser beam machining is employed for patterning each electrode in the manufacture of the known photoelectric conversion apparatus, there is a need to pattern only the electrodes located on one surface of the substrate. In order to avoid any damage of thin film(s) on the opposite surface of the substrate due to a laser beam transmitted through the substrate, it is required to select the material of the substrate from those having a low transmittance to laser beams, or select an appropriate type of laser beam, or control its power. For the same reason, there is a limit to the construction or shape of electrodes films.